In heat exchangers for vehicles (such as evaporators and condensers) and heat exchangers for home use (such as water heaters and air conditioners), members produced by, for example, brazing (joining) aluminum or aluminum alloy members to each other have been used.
Specifically, for example, a heat exchanger for a vehicle is formed by joining tubes, fins, side plates, a tank, etc., made of aluminum or an aluminum alloy by brazing.
Generally, to braze such components, a brazing composition containing a flux, a binder resin, and, if necessary, a brazing material etc. is used. Specifically, for example, a flux composition for brazing of an aluminum material has been proposed, which is obtained by dispersing 1 to 60% by weight, based on the total dry weight of the flux composition, of a flux in an aqueous solution containing 1.0 to 20% by weight, on a dry weight basis, of a water-soluble organic resin such as a water-soluble acrylic resin or a water-soluble polyurethane resin and further containing at least one of a curing agent and a surfactant (see Patent Literature 1 below (Examples 1 and 2)).
Generally, such a flux composition for brazing of an aluminum material is applied to brazing portions of various components and is heated after these components are assembled. The binder resin is thereby thermally decomposed, and the components are brazed (joined).
If the binder resin is not thermally decomposed sufficiently, incomplete decomposition products (such as compounds having carbon-carbon bonds) are mixed into the decomposition gas. However, when the space between components to be brazed is large and is in an open state (an open space), the decomposition gas is released to the air.